Disconnect vacuum distributor engine dies - Vintage Mustang Forums

 
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post #1 of 9 (permalink) Old 04-21-2017, 11:23 AM Thread Starter
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Disconnect vacuum distributor engine dies

Yesterday I was going to time the engine disconnected the vacuum from the distributor plugged the vacuum port engine would just die had to set fast idle to 2000 rpm to keep it running. Hooked vacuum back up ran fine at idle with the cam I have idle is 1000-1100 rpm. Took it for a short ride ran like crap when I opened the secondaries it popped and sputtered.

It was running a little rich is why I went through things again secondary float was to high, checked total timing at 3000 rpm 45 degrees don't know how that happened reduced total timing to 34 degrees. It still won't run if vacuum is disconnected from distributor.

Using Pertronix ignition all I can think of is the vacuum advance can might be bad. Waiting on some new gaskets for the carb I tore the float setting gasket now leaking fuel new ones won't be here till Sunday.

I'm lost any ideas?

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post #2 of 9 (permalink) Old 04-21-2017, 12:12 PM
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Initial advance is off.might have an issue with total advance also. You have to set timing with vacuum disconnected. Disconnect vacuum, twist distributor slightly clockwise and try to start engine, then set base timing. Then reconnect vacuum, note timing now and bring speed up to 2500 to check total timing.

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post #3 of 9 (permalink) Old 04-21-2017, 12:25 PM
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Sounds like you have the vacuum advance connected to manifold vacuum. While there is a use for that, the factory NEVER did it that way. Ford connected the advance to ported vacuum, which does not exist at idle, so disconnecting it should have no effect whatsoever.

Factory engine vacuum diagrams

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post #4 of 9 (permalink) Old 04-21-2017, 12:39 PM Thread Starter
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I'm using a ported vacuum source.

I disconnected the ported vacuum and put a cap on it, tried to start it it wouldn't stay running under 2000 rpm.

Hooked vacuum back up to distributor and it started and idled at 1000 rpm.

Base is set at 10*

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post #5 of 9 (permalink) Old 04-21-2017, 01:28 PM
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Originally Posted by Bob & Sue View Post
I disconnected the ported vacuum and put a cap on it, tried to start it it wouldn't stay running under 2000 rpm.
Im thinking this is bringing in the centrifugal advance=add more base. See if it is completely off at the idle screw=carb at full idle spec=no vacc
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post #6 of 9 (permalink) Old 04-21-2017, 02:26 PM
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If you need 1000 rpms to idle, a "stock" vacuum advance distributor just won't work for you. Check your idle vacuum. My guess would be it is down in the range of around 8 if this is a small block or maybe 12 or 13 for a larger engine and that is the why.

Your engine won't even crank up and idle with the 6 or 7 or whatever(10) low idle advance a vacuum type distributor provides. You will need a lot more initial timing for idle like a minimum of 18 and 20 to 24 will make it happier. The reason it will crank with the vacuum hooked up is that with that low an idle vacuum, the ported vacuum is putting on some of the vacuum advance at idle.

You will either have to send off your vacuum distributor to have it custom configured or switch to a mechanical only advance distributor that you can get a springs and advance stop kit for. I highly recommend the not cheap but very nice mechanical advance MSD pro billet distributor. I've been running these for years now. It requires an MSD ignition box though.

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Last edited by macstang; 04-21-2017 at 02:53 PM.
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post #7 of 9 (permalink) Old 04-21-2017, 04:15 PM
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Before throwing money at your problem, check the basics.


1) Verify that the vacuum canister holds a vacuum meaning the diaphragm is not torn. Do a quick search on youtube for videos checking these.


2) Remove your distributor cap, and apply vacuum pressure to your vacuum advance canister. Watch your points plate. This should cause it to move. This movement advances the timing when the engine is idling and cruising without load. (The idling timing will be impacted only if connected to manifold vacuum)


3) Verify your base timing really is 10 degrees btdc like you believe. Remember this is measured without the vacuum advance connected. If you check your timing with the vacuum advance connected, it should register greater than the base timing.


I suspect that at least number 3 above is not right. Perhaps items 1 and 2 need attention as well. After all, these checks are easy to do and may shine light on your issue.

Last edited by Rufus68; 04-21-2017 at 04:18 PM.
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post #8 of 9 (permalink) Old Yesterday, 10:00 AM Thread Starter
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Thanks for all the replies,

After installing the new secondary float adjusting kit (remember to loosen screw before turning nut unless you want to rip a gasket and leak fuel) the secondary float was set way to high after raising the float till it was just below the sight glass I was able to get it to idle at 850 rpm with a Mac auto tach my Sunn tach turns out to be off a couple hundred rpm at idle.

Set the base timing to 12* with vacuum disconnected no problems this time.

I must have set the secondary float high by mistake when it was idling rough with vacuum disconnected I could see raw fuel in the carb must be why it wouldn't idle under 2000 rpm.

Took it out for an hour test ride runs and starts great again.

I have it on manifold vacuum now instead of the ported carb port I'm going to leave it alone.

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post #9 of 9 (permalink) Old Yesterday, 09:10 PM
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If you're using ported vacuum and have vacuum at idle your primary throttle plates are open too far. If so, you have bigger issues, most likely related to your choice of camshaft or, potentially, valve timing or adjustment (too much preload).

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